The options for studying solid and gas interactions in an electron microscope are limited to a couple of types of systems. Commercially available environmental scanning/transmission electron microscope (ESEM/ETEM) technologies create a gaseous environment close to the object under investigation and enable the atomic scale study of phenomena occurring during gas-solid interactions. This gas environment is typically limited to low pressures of less than 15 Torr. Alternatively, for pressures up to 760 Torr or higher, special gas sample holders, called “environmental sample holders,” create a sealed gas environment and utilize membranes transparent to the electron beam to enable the atomic scale study.
The sample holder is a component of an electron microscope providing the physical support for samples under observation. Sample holders traditionally used for TEMs and STEMs, as well as some modern SEMs, consist of a rod that is comprised of three key regions: the end, the barrel and the specimen tip. In addition to supporting the sample, the sample holder provides an interface between the inside of the instrument (i.e., a vacuum environment) and the outside world.
To use the sample holder, one or more samples are first placed on a sample support device. The sample support device is then mechanically fixed in place at the specimen tip, and the sample holder is inserted into the electron microscope through a load-lock. During insertion, the sample holder is pushed into the electron microscope, assisted by the vacuum within the microscope, until it stops, which results in the specimen tip of the sample holder being located in the column of the microscope. At this point, the barrel of the sample holder bridges the space between the inside of the microscope and the outside of the load lock, and the end of the sample holder is outside the microscope. To maintain an ultra-high vacuum environment inside the electron microscope, flexible o-rings are typically found along the barrel of the sample holder, and these o-rings seal against the microscope when the sample holder is inserted. The exact shape and size of the sample holder varies with the type and manufacturer of the electron microscope, but each holder contains the three aforementioned key regions.
The sample holder can also be used to provide stimulus to the sample, and this stimulus can include temperature (e.g., heating or cooling), electricity (e.g., applying a voltage or current), mechanical (e.g., applying stress or strain), gas or liquid (e.g., containing a sample in a specific gaseous or liquid environment), or several at once. For example, a gas delivery system can be used to move gas to a sample during imaging. This equipment is outside of the microscope, and various connectors are used to bring this stimulus to the sample holder, down the length of the holder, and to the samples. For example, microfluidic tubing can be used to supply gas from a gas delivery system to the sample.
One configuration is an environmental cell wherein two semiconductor devices comprising thin windows are used, and samples are sandwiched between the two semiconductor devices, and the environment in proximity of the sample, including an electrical field and a gas or liquid flow, can be precisely controlled. The present applicant previously described novel apparatuses and methods to contact and align devices used to form liquid or gas cells in International Patent Application No. PCT/US2011/46282 filed on Aug. 2, 2011 entitled “ELECTRON MICROSCOPE SAMPLE HOLDER FOR FORMING A GAS OR LIQUID CELL WITH TWO SEMICONDUCTOR DEVICES,” which is hereby incorporated herein by reference in its entirety.
Disadvantageously, to date, environmental sample holders have had only limited availability, in part because these holders have lacked a gas delivery system with the necessary safety controls.
Environmental sample holders typically require the user to flow a gas or gases of interest into and out of the holder. The electron microscope requires a high vacuum to function, and therefore a leak from the gas sample holder into the microscope would be problematic. For example, the leak would contaminate components inside the microscope. A worse case event would be irreparable damage to the FEG (Field Emission Gun). Therefore, it is important to have a system that can detect and/or prevent and/or stop gas leaks inside the electron microscope that could cause damage.
Furthermore, the gas being delivered to the holder could be harmful if exposed to the environment outside of the microscope. For example, a toxic gas leaked into the environment could harm a person or a volatile gas could result in a fire or explosion. Therefore, it is important to have a system that can detect and/or prevent and/or stop gas that could be dangerous (toxic or volatile) from entering the human environment.
Additionally, combining two or more dissimilar gases together may not be safe as it could result in a reaction and/or a harmful mixture. A system that can prevent mixing of gases from occurring, until desired, will make a gas delivery system inherently safer.
Accordingly, a gas delivery system that can detect and react safely to leaks and other gas safety issues is needed and is described herein.